The Shimmer3 GSR+ (Galvanic Skin Response) monitors skin conductivity between two reusable electrodes attached to two fingers of one hand. Caused by a stimulus the sweat glands become more active, increasing moisture on the skin and allowing the current to flow more readily by changing the balance of positive and negative ions in the secreted fluid (increasing skin conductance).
The Shimmer3 GSR+ unit can also provide a photoplethysmogram (PPG) signal from a finger, ear-lobe, or other location on the body when adding an Optical Pulse probe.
Shimmer is a widely used and trusted product with a long publication history. Find white papers, research papers and more here: https://shimmersensing.com/support/publications/